Question

Heterogametic sex determination based on the number of sex chromosomes among the following are
A) XX-XO and XX-XY methods
B) ZO-ZZ and ZW-ZZ methods
C) XX-XY and ZW-ZZ methods
D) XX-XO and ZO-ZZ methods

Answer 1

Hint:Heterogametic sex determination is defined as a sex that has sex chromosomes that differ in morphology. It produces different types of gametes. In mammals and most other animals the male is the heterogametic.

Complete answer:
>In humans the male has X and Y chromosomes so it is referred as heterogametic sex.
>The females have two X sex chromosomes so referred as homogametic sex.
>The ZW sex determination system is a chromosomal system of sex determination in birds, some fish, some insects and reptiles.
>In this system the females have a pair of dissimilar ZW chromosomes that are heterogametic.
>The males have two similar ZZ chromosomes that are homogametic.
>In the ZW system the ovum determines the sex of the offspring while in the XY sex determination system the sperm determines the sex.
>The heterogametic can result in reduced or absent meiotic recombination.
>The homogametic sex has sex chromosomes that match and produce the same gametes.

Hence the correct answer is XX-XY and ZW-ZZ methods.

Note:The males are not always heterogametic. The females are heterogametic in birds, moths and fish. The chromosomal sex is determined at the time of fertilization.The chromosomes are the thread-like structures which are found inside the nucleus of plant and animal cells. Humans have 23 pairs of chromosomes. The 22 pairs are autosomes while 1 pair is of sex chromosomes.